The present invention relates to an electromagnetic actuator having a rotor that rotates within a predetermined angular range and relates to a camera shutter device that uses such an electromagnetic actuator as its drive source.
Electromagnetic actuators used as drive sources for a camera shutter devices, particularly focal-plane type camera shutter devices are known from, for example, Unexamined Japanese Patent Gazettes No. 1-310329, No. 8-190123 (corresponding to U.S. Pat. No. 5,749,014), No. 8-254729, No. 9-329827, and No. 10-20364 (corresponding to U.S. Pat. No. 6,071,019), and U.S. Pat. Nos. 5,822,629 and 6,000,860.
The electromagnetic actuators disclosed in the gazettes or the like comprise a rotor with a cylindrical permanent magnet that outputs a rotational driving force, a frame member that rotatably supports the rotor, and a coil wound around the outside of the frame member.
These electromagnetic actuators are arranged on the base plate as drive sources for camera shutter devices so that the actuators are set correspondingly with before-moving (or first-moving) and after-moving (or second-moving) shutter blades, and open and close the aperture for exposure by driving the before-moving and after-moving shutter blades respectively through a complex interlocking mechanism including a drive lever.
The shutter devices are also provided with a stopper mechanism that positions the shutter blades at the operation start position before the shutter blades start moving for the exposure operation and a brake mechanism that prevents bounds or the like of the shutter blades at the completion of the movement.
In the conventional electromagnetic actuator, the coil is wound around the outside of the rotor in the direction of the rotation axis of the rotor so as to surround the axis, thereby increasing the height or the thickness of the electromagnetic actuator.
Therefore, if the actuator is used as a drive source for a focal-plane camera shutter device to be incorporated particularly in a camera or the like required for thinness, the freedom of its arrangement is limited due to its great height (thickness). As a result, it is difficult to produce a thin camera with the actuator.
The camera shutter devices disclosed in Unexamined Japanese Patent Gazettes No. 8-190123 (corresponding to U.S. Pat. No. 5,749,014) and No. 10-20364 (corresponding to U.S. Pat. No. 6,071,019) adopt an electromagnetic actuator composed of flat yokes, a coil wound around the yokes and a rotor placed between the yokes, and use the actuator as a trigger mechanism to release the before-moving and after-moving shutter blades engaged and stopped. The devices are designed to move the before-moving and after-moving shutter blades by releasing the spring force charged by the complex charging mechanism.
Therefore, the devices use complex mechanisms such as a charging mechanism, a trigger mechanism (engagement and stop release mechanism) or the like, thereby increasing the number of parts used and complicating their structures. As a result, the device becomes large and the cost is increased accordingly.
The present invention is made in view of the problems. The purpose of the present invention is to provide an electromagnetic actuator that enables the simplification of the structure, low power consumption and thinning of the device as well as a camera shutter device with such an actuator and even a camera shutter device that gives a desired stable exposure operation.
The electromagnetic actuator in the present invention comprises an exciting coil, a yoke forming a magnetic circuit and a rotatable rotor which is magnetized with different polarities, rotates within a predetermined angular range through the supply of current to the coil, and has an output portion to output the driving force externally. The yoke comprises flat plate-like yokes provided with first and second magnetic pole parts formed to be opposed to the circumference surface of the rotor. The coil comprises first and second coils wound in such a manner that different polarities are generated in the first and second magnetic pole parts and the coils become flat in the same direction as the plate-like yoke when the current is turned.
According to this configuration, when the first and second coils are supplied with electricity, generated lines of magnetic force pass through the plate-like yokes and cause the generation of different poles (north pole in one part and south pole in the other part) in the first and second magnetic pole parts, and then, by the relationship between the rotor""s magnetic pole (north pole and south pole) and the generated poles, the rotor rotates within the predetermined angular range and outputs the driving force externally.
As shown above, the electromagnetic actuator is composed of a flat plate-like yoke and first and second coils wound flat, thereby increasing the driving force and at the same time, making the device thin (flat).
Herein, the plate-like yoke may be laminated with a plurality of magnetic plates in the direction of the rotation axis of the rotor.
According to this configuration, a plate-like yoke whose thickness conforms to various specifications by selecting the suitable number of magnetic plates for lamination as required can be formed.
In addition, the plate-like yoke may be divided into two parts, which are of a first yoke having a first magnetic pole part and a second yoke having a second magnetic pole part, in the direction substantially perpendicular to the rotor""s rotation axis. The first and second coils may be wound around the joint areas of the first and second yokes, respectively.
According to this configuration, the assembly efficiency is improved by dividing the plate-like yoke into two parts. The bobbin, etc. that winds the coils can also serve as a member for joint by winding the first and second coils around the joint areas of the first and second yokes. Furthermore, the number of part types is decreased by making the divided first and second yokes identical in shape, whereby the management cost, etc. can be reduced.
The first and second yokes may be jointed at least on the planes overlapping in the direction of the rotor""s rotation axis.
If a yoke whose thickness in the direction of the rotor""s rotation axis is thin is used and the two divided yokes are jointed in the direction perpendicular to the rotor""s rotation axis, enough joint area can not be obtained due to the thin plate. According to this configuration, however, the enough joint area for the two yokes can be obtained by jointing them on the planes overlapping in the direction of the rotor""s rotation axis. That is to say, the magnetic efficiency on the interface of the two-divided yokes can be enhanced while the yokes can be thinned.
The first and second yokes may be jointed to get engaged with each other on the planes alternately overlapping in the direction of the rotor""s rotation axis.
According to this configuration, the magnetic efficiency on the interface can be enhanced while the yokes can be thinned, as shown above. Moreover, since the first and second yokes are jointed to engage with each other by overlapping them alternately, sufficient joint strength can be obtained even though a thin plate is used as the laminated magnetic plate.
The first and second coils are arranged opposite each other with the rotor sandwiched therebetween. The first and second magnetic pole parts are arranged opposite each other in the direction substantially perpendicular to the direction that the first and second coils are arranged opposite each other, and have a constricted portion formed by narrowing down the cross section as the magnetic circuit, compared with the other portions.
According to this configuration, the lines of magnetic force generated by the first and second coils affect the first and second magnetic pole parts differently with the constricted portion as the boundary of their influence. By this effect, an efficient magnetic circuit is formed and the rotor can efficiently generate a rotary driving force.
A substantially semi-cylindrical opposite surface opposed to the rotor may be formed on the first and second magnetic pole parts, while the constricted portions may be formed on the middle portions (that is, the areas corresponding to the middle portions in the direction of the circumference of the opposite surfaces) of the first and second magnetic pole parts.
According to this configuration, the first and second magnetic pole parts supply a greater electromagnetic force to the rotor and the respective lines of magnetic force generated by the first and second coils act on the rotor symmetrically, and therefore, the rotor can generate a stable rotary driving force.
The camera shutter device in the present invention is provided with a shutter blade that opens and closes the aperture for exposure and a drive source that drives the shutter blade. This drive source is an electromagnetic actuator that includes an exciting coil, a yoke forming a magnetic circuit, and a rotatable rotor that is magnetized with different polarities, rotates within the predetermined angular range and has an output portion outputting the driving force externally when the coil is supplied with current. The yoke is composed of flat plate-like yokes that have respective first and second magnetic pole parts opposed to the peripheral surface of the rotor. The coil is composed of first and second coils wound in such a manner that different polarities are generated in the first and second magnetic pole parts and the coils become flat in the same direction as the plate-like yoke.
According to this configuration, by using a thinned (flat) electromagnetic actuator as the drive source, a camera shutter device can be thinned, and therefore, a camera that incorporates such a camera shutter device can also be thinned.
Herein, the shutter blade may be composed of a before-moving blade and an after-moving blade that open and close the aperture by substantially linear reciprocating motion, while the drive source may be composed of first and second electromagnetic actuators to drive the before-moving and after-moving blades, respectively.
According to this configuration, a focal-plane type shutter device that is equipped with the before-moving and after-moving blades as a shutter blade can be thinned.
The first and second electromagnetic actuators may be arranged on both sides sandwiching the aperture, arranged by lining on one side of the aperture, or arranged by lining parallel to each other in the longitudinal direction on one side of the aperture.
According to this configuration, if the electromagnetic actuators are arranged on both sides sandwiching the aperture, for example, a digital still camera or the like that requires no storage space for film cartridges can be further thinned by arranging one of the electromagnetic actuators in the portion corresponding to the storage space. On the other hand, if the electromagnetic actuators are arranged on one side of the aperture, parts-intensive configuration can be made and the width of a camera can be narrowed, and therefore, the camera can be miniaturized. If the electromagnetic actuators are arranged parallel to each other particularly in the longitudinal direction, the width of the camera can be reduced vertically.
Herein, the electromagnetic actuator may be an actuator urged magnetically to enable the shutter blade to keep the aperture closed in the non-energized condition, an actuator urged magnetically to enable the shutter blade to keep the aperture opened in the non-energized condition, or an actuator urged magnetically to enable the shutter blade to keep the aperture closed and keep the aperture opened in the non-energized condition.
According to these configurations, a desired shutter function can be obtained while power consumption is reduced.
The shutter blade may be composed of first and second shutter blades that open and close the aperture by reciprocating motion, while the drive source may be of a single electromagnetic actuator that drives the first and second shutter blades.
According to this configuration, by using a single thinned (flat) electromagnetic actuator as the drive source, for example, the lens shutter device, etc. disposed in the lens barrel of a camera can be thinned (made flat).
The camera shutter device in the present invention includes a shutter blade that opens and closes the aperture for exposure, such an electromagnetic actuator as above that directly drives the shutter blade as a drive source to move it for exposure operation, and a control means for controlling current supply for the drive source.
The control means may control current supply in the direction reverse to the direction of moving the shutter blade for the drive source in order to position the shutter blade immediately before the blade is moved, control current supply for the electromagnetic drive source so that electric power is lower in the area where the shutter blade is on the move after starting moving than in the area where the shutter blade starts moving, or control current supply in the direction reverse to the direction of moving the shutter blade for the drive source immediately before the shutter blade completes the movement.
According to this configuration, by controlling current supply in the reverse direction immediately before the blade moves, a reverse biasing force is generated by the electromagnetic drive source, and the shutter blade starts moving in the condition that the shutter blade is securely positioned at the operation (movement) starting position. By this effect, the exposure operation becomes stable. By controlling current supply so that electric power is low in the area where the blade is on the move, the shutter blade continues moving due to its inertia force, thereby reducing the power consumption required to drive the shutter blade. Furthermore, by controlling current supply in the reverse direction immediately before the blade completes the movement, the electromagnetic drive source generates the reverse driving force to brake the shutter blade moving due to its inertia force, thereby preventing a bound phenomenon, etc. when the blade stops after hitting the stopper or the like. As a result, the shutter blade stops promptly, and the time required for a single exposure operation is shortened and high-speed successive photography, etc. can be performed.
Herein, in order to control current supply for low electric power in the area where the blade is on the move, the means may control current supply by lowering the value of the current supplied or control current supply by pulse. According to this configuration, by a simple control method, the shutter blade can perform stable exposure operations while the power consumption is reduced.
In the device, the shutter blade may be composed of a before-moving blade and an after-moving blade that open and close the aperture by reciprocating motion, an electromagnetic actuator may be composed of a before-moving blade electromagnetic actuator to drive the before-moving blade and an after-moving blade electromagnetic actuator to drive the after-moving blade, and the means may control the current supply as above for the before-moving blade and after-moving blade electromagnetic actuators.
According to this configuration, by a series of current supply control mentioned above is made for the before-moving blade and after-moving blade electromagnetic actuators, for example, in a focal-plane type camera shutter device, power consumption is reduced, a bound phenomenon or the like is prevented and stable exposure operations can be performed by the before-moving blade and after-moving blade.
In addition, in the device, the shutter blade may be composed of first and second shutter blades that open and close the aperture by reciprocating motion, the electromagnetic actuator may be composed of a first electromagnetic actuator to drive the first shutter blade and a second electromagnetic actuator to drive the second shutter blade, and the control means may control the current supply for the first and second electromagnetic actuators in such a manner that the first shutter blade moves as a before-moving blade and the second shutter blade moves as an after-moving blade, and then, the second shutter blade moves as a before-moving blade and the first shutter blade moves as an after-moving blade.
According to this configuration, the first and second shutter blades serve alternately as a before-moving blade and an after-moving blade, whereby it is possible to make it unnecessary for the shutter blades to perform the return operation after their complete movement, simplify the control sequence and increase the frequency of successive photography if required.